A differential impulse conveyor includes a generally elongate horizontal or slightly inclined tray or pan having a planar surface for transporting goods thereon. The tray is moved slowly forward to convey the goods with respect to the tray and is then pulled rearward at a high return speed so that the goods slide along the tray, thereby effectively transporting the goods along the conveyor tray. Differential impulse conveyors, which are sometimes referred to as linear motion conveyors, are operationally distinguishable from other types of conveyors, such as reciprocating conveyors, shuffle conveyors, vibrating conveyors, or shaker conveyors. A significant advantage of differential impulse conveyors is that goods may be transported along the unitary tray (no moving tray parts) in a manner that does not tend to damage fragile goods. Differential impulse conveyors have thus been preferred in many applications, such as food handling, when conveyor cleanliness, low noise, and minimal product damage are desired.
The drive mechanism of a differential impulse conveyor generates repeated acceleration and deceleration of the tray. Inherently the forward acceleration is lower than the rearward acceleration so that goods slide along the tray substantially only when the tray is pulled rearward at a high return speed. One type of prior art mechanism for driving a differential impulse conveyor includes a plurality of flywheels suspended from the conveyor tray such that the momentum of the rotating flywheels achieves the desired slow forward speed and high return speed for the conveyor tray. This flywheel drive mechanism is costly and cannot be easily optimized to adjust the ratio of the forward speed and return speed to achieve the desired product speed along the conveyor tray.
An improved differential conveyor is disclosed in U.S. Pat. No. 5,351,807 ('807 patent). The drive mechanism of this conveyor employs an angled universal joint in combination with a 1:2 speed enhancer to achieve one half cycle rotation of a drive shaft at a slow speed followed by one half cycle rotation of the drive shaft at a high speed. A crank interconnects the drive shaft and the tray to achieve the desired conveyor movement. The angle of the universal joint and the speed of the motor may be adjusted to maximize product travel along the conveyor tray. A counterweight is also driven by the drive shaft to move 180.degree. out of phase with the conveyor tray movement, thereby substantially reducing undesirable conveyor vibration and mechanical knock in the drive system. A hydraulic fluid pump may also be driven by the drive shaft to serve a dampening function and further reduce knock in the drive mechanism.
Although the techniques disclosed in the '807 patent have significantly advanced the acceptance of differential impulse conveyors, improvements to further reduce or eliminate mechanical knock in the drive system are desired. Hydraulic dampening is not preferred for many food processing applications, wherein hydraulic fluid is avoided due to contamination and safety concerns. By further reducing mechanical knock in the drive mechanism, the size and thus the cost of conveyor drive components may be reduced without adversely affecting the useful life of the conveyor. In some applications, it may be desirable to drive the conveyor with a motor rotating a shaft at a speed much higher than the speed desired for the varying half cycle drive shaft. Optimization of the drive mechanism will further enhance acceptance of differential impulse conveyors as a practical alternative to reciprocating conveyors, shuffle conveyors, vibrating conveyors, and shaker conveyors.
Another problem with conveyors designed to move goods along a substantially horizontal surface of a tray by either differential impulse or vibration techniques concerns the difficulty with moving the pan so that the area beneath the tray may be easily cleaned. While the drive mechanism is typically detachable from the conveyor tray, a good deal of time and expertise is required to detach the drive mechanism from the tray, move the tray away from the drive mechanism for cleaning, then reattach the drive mechanism to the tray. Also, conveyor pans supplying goods to scales or weighers require precise positioning of the pan for optimal feeding of the scale or weigher. In order to reduce the time required for cleaning the area beneath the tray, the entire conveyor including the tray and drive mechanism have been movably supported on rails. The conveyor assembly weighing in excess of several thousand pounds may thus be rolled out along the rails for cleaning, then rolled back into its proper position with respect to the scale. Considerable expense is thus expended to move the conveyor for cleaning, then to properly reposition the conveyor with respect to the scale.
The disadvantages of the prior art are overcome by the present invention. An improved differential impulse conveyor and the drive mechanism for a differential impulse conveyor which desirably reduces mechanical knock are hereinafter disclosed. The drive mechanism optionally allows the motor shaft to be rotated at a speed much greater than the drive shaft, thereby reducing the cost of the conveyor drive mechanism.